arXiv subjects

M. I. Gorenstein

Publications and source records attributed to M. I. Gorenstein.

At least 37 records · Page 2Linked to original sources

arXiv2018

Ultrasonic waves in classical gases

The velocity and absorption coefficient for the plane sound waves in a classical gas are obtained by solving the Boltzmann kinetic equation, which describes the reaction of the single-particle distribution function to a periodic external field. Within the linear response theory, the nonperturbative dispersion equation valid for all sound frequencies is derived and solved numerically. The results are in agreement with the approximate analytical solutions found for both the frequent- and rare-collision regimes.

cond-mat.stat-mech↗

arXiv2018

Nucleon matter equation of state, particle number fluctuations, and shear viscosity within UrQMD box calculations

Properties of equilibrated nucleon system are studied within the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) transport model. The UrQMD calculations are done within a finite box with periodic boundary conditions. The system achieves thermal equilibrium due to nucleon-nucleon elastic scattering. For the UrQMD equilibrium state, nucleon energy spectra, equation of state, particle number fluctuations, and shear viscosity $η$ are calculated. The UrQMD results are compared with both, statistical mechanics and Chapman-Enskog kinetic theory, for a classical system of nucleons with hard-core repulsion.

nucl-th↗

arXiv2017

Quantum van der Waals and Walecka models of nuclear matter

A comparable study of the quantum van der Waals and Walecka models of nuclear matter is presented. Each model contains two parameters which characterize the repulsive and attractive interactions between nucleons. These parameters are fixed in order to reproduce the known properties of the nuclear ground state. Both models predict a first-order liquid-gas phase transition and a very similar behavior in the vicinity of the critical point. Critical exponents of the quantum van der Waals model are studied both analytically and numerically. There are important differences in the behavior of the thermodynamical functions of the considered models at large values of the nucleon number density. At the same time both models fall into the universality class of mean-field theory.

nucl-th↗

arXiv2017

Open charm production in central Pb+Pb collisions at the CERN SPS: statistical model estimates

Charm particle production in nucleus-nucleus collisions at the CERN SPS energies is considered within a statistical approach. Namely, the Statistical Model of the Early Stage is used to calculate mean multiplicity of charm particles in central Pb+Pb collisions. A small number of produced charm particles necessitates the use of the exact charm conservation law. The model predicts a rapid increase of mean charm multiplicity as a function of collision energy. The mean multiplicity calculated for central Pb+Pb collisions at the center of mass energy per nucleon pair $\sqrt{s_{NN}}=17.3$ GeV exceeds significantly the experimental upper limit. Thus, in order to describe open charm production model parameters and/or assumptions should be revised.

nucl-th↗

arXiv2017

Bose-Einstein condensation and liquid-gas phase transition in alpha-matter

Systems of Bose particles with both repulsive and attractive interactions are studied using the Skyrme-like mean-field model. The phase diagram of such systems exhibits two special lines in the chemical potential-temperature plane: one line which represents the first-order liquid-gas phase transition with the critical end point, and another line which represents the onset of Bose-Einstein condensation. The calculations are made for strongly-interacting matter composed of alpha particles. The phase diagram of this matter is qualitatively similar to that observed for the atomic He4 liquid. The sensitivity of the results to the model parameters is studied. For weak interaction coupling the critical point is located at the Bose-condensation line.

nucl-th↗

arXiv2017

Workshop on Excited Hyperons in QCD Thermodynamics at Freeze-Out (YSTAR2016) Mini-Proceedings

This Workshop brought top experts, researchers, postdocs, and students from high-energy heavy ion interactions, lattice QCD and hadronic physics communities together. YSTAR2016 discussed the impact of "missing" hyperon resonances on QCD thermodynamics, on freeze-out in heavy ion collisions, on the evolution of early universe, and on the spectroscopy of strange particles. Recent studies that compared lattice QCD predictions of thermodynamic properties of quark-gluon plasma at freeze-out with calculations based on statistical hadron resonance gas models as well as experimentally measured ratios between yields of different hadron species in heavy ion collisions provide indirect evidence for the presence of "missing" resonances in all of these contexts. The aim of the YSTAR2016 Workshop was to sharpen these comparisons and advance our understanding of the formation of strange hadrons from quarks and gluons microseconds after the Big Bang and in todays experiments at LHC and RHIC as well as at future facilities like FAIR, J-PARC and KL at JLab. It was concluded that the new initiative to create a secondary beam of neutral kaons at JLab will make a bridge between the hardron spectroscopy, heavy-ion experiments and lattice QCD studies addressing some major issues related to thermodynamics of the early universe and cosmology in general.

hep-ph↗

arXiv2017

Missing resonance decays in thermal models

Detailed information on decay channel probabilities is absent for many high mass resonances, which are typically included in thermal models. In these cases, the sum over all known decay branching probabilities is smaller than 1. Due to this systematic uncertainty of the model, the exact charge conservation may appear to be violated. We estimate the corresponding number of missing charge states in the canonical ensemble formulation of the hadron resonance gas for p+p reactions at the SPS energy $E_{\rm lab}=158$ GeV: $ΔB \simeq 0.16$ for baryon charge, $ΔQ\simeq 0.12$ for electric charge, and $ΔS=-0.01$ for strangeness. The value of the considered effect is 5-8%, which seems to be important enough to include it as a systematic error in the calculations within a hadron gas.

nucl-th↗

arXiv2016

Shear viscosity of nuclear matter

Shear viscosity $η$ is calculated for the nuclear matter described as a system of interacting nucleons with the van der Waals (VDW) equation of state. The Boltzmann-Vlasov kinetic equation is solved in terms of the plane waves of the collective overdamped motion. In the frequent-collision regime, the shear viscosity depends on the particle-number density $n$ through the mean-field parameter $a$, which describes attractive forces in the VDW equation. In the temperature region $T=15 - 40$~MeV, a ratio of the shear viscosity to the entropy density $s$ is smaller than 1 at the nucleon number density $n =(0.5 - 1.5)\,n^{}_0$, where $n^{}_0=0.16\,$fm$^{-3}$ is the particle density of equilibrium nuclear matter at zero temperature. A minimum of the $η/s$ ratio takes place somewhere in a vicinity of the critical point of the VDW system. Large values of $η/s\gg 1$ are, however, found in both the low-density, $n\ll n^{}_0$, and high-density, $n>2n^{}_0$, regions. This makes the ideal hydrodynamic approach inapplicable for these densities.

nucl-th↗

arXiv2016

New scenarios for hard-core interactions in a hadron resonance gas

The equation of state of a baryon-symmetric hadronic matter with hard-sphere interactions is studied. It is assumed that mesons are point-like, but baryons and antibaryons have the same hard-core radius rB. Three possibilities are considered: 1) the baryon-baryon and antibaryon-baryon interactions are the same; 2) baryons do not interact with antibaryons; 3) the baryon-antibaryon and meson-(anti)baryon interactions are negligible. By choosing the parameter rB=0.3-0.6 fm, we calculate the nucleon to pion ratio as a function of temperature and perform the fit of hadron yields measured in central Pb+Pb collisions at the bombarding energy Ecm=2.76 TeV per nucleon pair. New nontrivial effects in the interacting hadron resonance gas at temperatures 150-200 MeV are found.

nucl-th↗

arXiv2016

Cumulative pion production via successive collisions in nuclear medium

Production of pions in proton-nucleus (p+A) reactions outside of a kinematical boundary of proton-nucleon collisions, the so-called cumulative effect, is studied. The kinematical restrictions on pions emitted in backward direction in the target rest frame are analyzed. It is shown that cumulative pion production requires a presence of massive baryonic resonances that are produced during successive collisions of projectile with nuclear nucleons. After each successive collision the mass of created resonance may increase and, simultaneously, its longitudinal velocity decreases. Simulations within Ultra relativistic Quantum Molecular Dynamics model reveals that successive collisions of baryonic resonances with nuclear nucleons plays the dominant role in cumulative pion production in p+A reactions.

nucl-th↗

arXiv2016

Critical fluctuations in models with van der Waals interactions

Particle number fluctuations are considered within the van der Waals (VDW) equation, which contains both attractive (mean-field) and repulsive (eigenvolume) interactions. The VDW equation is used to calculate the scaled variance of particle number fluctuations in generic Boltzmann VDW system and in nuclear matter. The strongly intensive measures $Δ[E^*,N]$ and $Σ[E^*,N]$ of the particle number and excitation energy fluctuations are also considered, and, similarly, show singular behavior near the critical point. The $Δ[E^*,N]$ measure is shown to attain both positive and negative values in the vicinity of critical point. Based on universality argument, similar behavior is expected to occur in the vicinity of the QCD critical point.

nucl-th↗

arXiv2016

Updates to the p+p and A+A chemical freeze-out lines from the new experimental data

We show that the new data on mean multiplicities measured in p+p and A+A collisions together with the updated list of resonances lead to the significant changes of the obtained freeze-out lines. The new A+A line gives much smaller temperatures at high collision energies and agrees with the values obtained at the LHC. The newly obtained p+p line is much closer to the A+A line than previously expected, and even touches it in the region where the $K^+/π^+$ horn appears in the data. It indicates that the temperatures that will be obtained in the beam energy and system size scan by the NA61/SHINE Collaboration might be very close. However, our analysis shows that the chemical potentials could be very different for the same energies in A+A and p+p. It adds more puzzles to the set of surprising coincidences at the energies close to the possible onset of deconfinement.

nucl-th↗

arXiv2016

Limiting temperature of pion gas with the van der Waals equation of state

The grand canonical ensemble formulation of the van der Waals equation of state that includes the effects of Bose statistics is applied to an equilibrium system of interacting pions. If the attractive interaction between pions is large enough, a limiting temperature $T_0$ emerges, i.e., no thermodynamical equilibrium is possible at $T>T_0$. The system pressure $p$, particle number density $n$, and energy density $\varepsilon$ remain finite at $T=T_0$, whereas for $T$ near $T_0$ both the specific heat $C=d\varepsilon/dT$ and the scaled variance of particle number fluctuations $ω[N]$ are proportional to $(T_0-T)^{-1/2}$ and, thus, go to infinity at $T\rightarrow T_0$. The limiting temperature corresponds also to the softest point of the equation of state, i.e., the speed of sound squared $c_s^2=dp/d\varepsilon$ goes to zero as $(T_0-T)^{1/2}$. Very similar thermodynamical behavior takes place in the Hagedorn model for the special choice of a power, namely $m^{-4}$, in the pre-exponential factor of the mass spectrum $ρ(m)$.

nucl-th↗

arXiv2016

Hydrodynamic modeling of a pure-glue initial scenario in high-energy hadron and heavy-ion collisions

Partonic matter produced in the early stage of ultrarelativistic nucleus-nucleus collisions is assumed to be composed mainly of gluons, and quarks and antiquarks are produced at later times. The comparable hydrodynamic simulations of heavy-ion collisions for (2+1)-flavor and Yang-Mills equations of state performed by using three different hydrodynamic codes are presented. Assuming slow chemical equilibration of quarks, the spectra and elliptic flows of thermal dileptons and photons are calculated for central Pb+Pb collisions at the LHC energy of $\sqrt{s_{_{\rm NN}}} = 2.76$ TeV. It is shown that a suppression of quarks at early times leads to a significant reduction of the yield of the thermal dileptons, but only to a rather modest suppression of the $p_T$-distribution of direct photons. It is demonstrated that an enhancement of photon and dilepton elliptic flows might serve as a promising signature of the pure-glue initial state. Calculations based on Bjorken hydrodynamics suggest that collisions of small systems at intermediate energies available at RHIC or future FAIR facilities may show stronger effects associated with initial pure gluodynamic evolution.

nucl-th↗

arXiv2016

Electromagnetic probes of a pure-glue initial state in nucleus-nucleus collisions at energies available at the CERN Large Hadron Collider

Partonic matter produced in the early stage of ultrarelativistic nucleus-nucleus collisions is assumed to be composed mainly of gluons, and quarks and antiquarks are produced at later times. To study the implications of such a scenario, the dynamical evolution of a chemically nonequilibrated system is described by the ideal (2+1)-dimensional hydrodynamics with a time dependent (anti)quark fugacity. The equation of state interpolates linearly between the lattice data for the pure gluonic matter and the lattice data for the chemically equilibrated quark-gluon plasma. The spectra and elliptic flows of thermal dileptons and photons are calculated for central Pb+Pb collisions at the CERN Large Hadron Collider energy of $\sqrt{s_{_{\rm NN}}} = 2.76$ TeV. We test the sensitivity of the results to the choice of equilibration times, including also the case where the complete chemical equilibrium of partons is reached already at the initial stage. It is shown that a suppression of quarks at early times leads to a significant reduction of the yield of the thermal dileptons, but only to a rather modest suppression of the $p_T$-distribution of direct photons. It is demonstrated that an enhancement of photon and dilepton elliptic flows might serve as a promising signature of the pure-glue initial state.

nucl-th↗

arXiv2016

Chemical freeze-out conditions in hadron resonance gas

The hadron resonance gas model with hadron-type dependent eigenvolume corrections is employed to fit the hadron yield data of the NA49 collaboration for central Pb+Pb collisions at the c.m. energy per nucleon pair Ecm=6.3, 7.6, 8.8, 12.3, and 17.3 GeV, the hadron midrapidity yield data of the STAR collaboration for Au+Au collisions at Ecm=200 GeV, and the hadron midrapidity yield data of the ALICE collaboration for Pb+Pb collisions at Ecm=2760 GeV. The influence of the eigenvolume corrections is studied.

hep-ph↗

arXiv2016

Hadron multiplicities and chemical freeze-out conditions in proton-proton and nucleus-nucleus collisions

New results of the NA61/SHINE Collaboration at the CERN SPS on mean hadron multiplicities in proton-proton (p+p) interactions are analyzed within the transport models and the hadron resonance gas (HRG) statistical model. The chemical freeze-out parameters in p+p interactions and central Pb+Pb (or Au+Au) collisions are found and compared with each other in the range of the center of mass energy of the nucleon pair $\sqrt{s_{NN}}=3.2-17.3$ GeV. The canonical ensemble formulation of the HRG model is used to describe mean hadron multiplicities in p+p interactions and the grand canonical ensemble in central Pb+Pb and Au+Au collisions. The chemical freeze-out temperatures in p+p interactions are found to be larger than the corresponding temperatures in central nucleus-nucleus collisions.

nucl-th↗

arXiv2016

Cumulative production of pions by heavy baryonic resonances in proton-nucleus collisions

Pion production in proton-nucleus (p+A) collisions outside the kinematical boundary of proton-nucleon (p+N) reactions, the so-called cumulative effect, is studied. Restrictions from energy-momentum conservation on the energy of pions emitted in the backward direction in the target rest frame are analyzed. It is assumed that the cumulative pions are produced in p+A reactions by heavy baryonic resonances. The baryonic resonances are first created in p+N reactions. Due to successive collisions with nuclear nucleons the masses of these resonances may then increase and, simultaneously, their longitudinal velocities decrease. We also use the Ultra relativistic Quantum Molecular Dynamics model to reveal the key role of successive collisions of baryonic resonances with nuclear nucleons for cumulative pion production in p+A reactions. Further experimental studies of cumulative hadron production in p+A reactions at high collision energies are needed to search for heavy hadron-like objects and investigate their properties.

hep-ph↗